Specifies a name for the attach to the database. Specifying an
    alias lets your program refer to more than one database.

    You do not have to specify an alias in the DECLARE ALIAS
    statement. The default alias in interactive SQL and in
    precompiled programs is RDB$DBHANDLE. In the SQL module language,
    the default is the alias specified in the module header. Using
    the default alias (either by specifying it explicitly in the
    DECLARE ALIAS statement or by omitting any alias) makes the
    database part of the default environment. Specifying a default
    database means that statements that refer to the default database
    do not need to use an alias.

    If a default alias was already declared and you specify the
    default alias in the alias clause (or specify any alias that
    was already declared), you receive an error when you precompile
    the program or process it with the SQL module processor.